You've got a few options here, but I'd say the easiest is by using the system expression Compare two values | distance(Player.X,Player.Y,Particle.X,Particle.Y) < DesiredDistance.

Alternatively you could use the Line of Sight behaviour and don't specify any blockers. If I'm not mistaken, LOS uses collision cell optimisation, so it'd be more efficient than the above method if your layout is quite large.